Plasma surface modification of polyimide films by air glow discharge for copper metallization on microelectronic flex substrates

Surface modification of polyimide films such as Kapton E(N) and Upilex S by air plasmas were investigated for enhanced adhesive strength with sputtered coppers. Peel tests demonstrate this improvement, with the peel strengths of 0.7 g/mm and 1.2 g/mm for unmodified Kapton E(N) and Upilex S and 99.3 g/mm and 91.5 g/mm for air plasma-modified Kapton E(N) and Upilex S at certain plasma conditions. This study reported that the enhanced adhesive strengths of polyimide films with sputtered coppers by air plasmas were strongly affected by the surface characteristics such as surface morphology and surface energy of polyimide films. Atomic force microscopy (AFM) and sessile drop method indicated the surface roughness and the surface energy of polyimide films were much increased by air plasmas that result in much increased peel strengths of polyimide films with sputtered coppers. Electron spectroscopy for chemical analysis (ESCA) observed the increased surface energy on polyimide films by air plasmas were due to the increased surface composition of O and the increased chemical bond of C–O.